What is contaminated land?

This page explains how contaminated land is defined under the Resource Management Act (RMA), how land can become contaminated, and when it becomes a problem.

Contaminated land definition

Contaminated land is defined under the RMA as land with hazardous substances in or on it that are reasonably likely to have significant adverse effects on the environment (including human health).

The full definition of contaminated land under section 2 of the RMA is:

“contaminated land means land that has a hazardous substance in or on it that –

has significant adverse effects on the environment; or

is reasonably likely to have significant adverse effects on the environment.”

How land becomes contaminated

Land can become contaminated when hazardous substances are not used, stored or disposed of in a safe way. Contamination is not always limited to a specific site. Hazardous substances may seep through the soil into groundwater, or be carried to nearby land and waterways in rainwater or as dust. Hazardous gases can also pollute the air.

The different pathways by which humans can be exposed to contaminants in soil are shown in the diagram below.

Read a textual description

This diagram shows the main pathways by which contaminants in soil can affect human health. The diagram depicts a rural residential setting with a house and home garden connected to roof water and groundwater supplies.

Cows are fenced behind the house and chickens are scratching and pecking in the garden. Adjacent to the house is a stream containing trout and eels. The house, garden, cows and chickens are shown located on contaminated soil.

Arrows show the pathways by which contaminants in soil can expose the human receptors directly or indirectly through food, air, soil and water. The human receptors in this diagram are a father and son in the garden, a mother and child wading in the stream, and an angler on the stream bank. The arrows describe the pathways as follows:

Primary pathways

Inhalation of dust

Soil contact (eating and skin absorption)

Secondary pathways

Crop uptake and eating of contaminated crops

Uptake by livestock and eating contaminated livestock

Surface water contact

Contaminant leaching/runoff pathways

Contaminant leaching to groundwater, uptake of contaminated groundwater by water supply bore, and drinking of contaminated water

Surface runoff from rainfall, uptake by aquatic animals, and eating of aquatic animals and surface water contact

Contaminant leaching to stream, uptake by aquatic animals, and eating of aquatic animals and surface water contact

Vapour intrusion into the house from contaminated soil.

Activities that have caused our land to become contaminated

The past use of hazardous substances in industry, agriculture and horticulture has left a legacy of soil contamination in New Zealand. This contamination has been mainly caused by past practices in which chemicals were used, stored and disposed of in a way that is not safe by today’s standards.

Contaminated sites are commonly associated with past activities such as:

Manufacture and use of pesticides – these activities have resulted in contamination at locations where pesticides were manufactured as well as the wider contamination associated with the use of the chemicals (eg, agrichemical sprays).

Production of gas and coal products – includes old gasworks sites located in most towns and cities.

Production, storage and use of petroleum products – contamination has occurred from leaking fuel storage facilities at tank farms and service stations.

Historic mining – usually associated with metals leaching from old tailings dams and mine shafts.

Timber treatment – pentachlorophenol (PCP) was one of a number of chemical formulations used routinely at most sawmills and timber treatment plants from the 1950s until 1988, when its use ceased.

Sheep dipping – from use of DDT, dieldrin, arsenic and other chemicals to treat parasites on sheep. Old sheep dips can be located on farms with a history of sheep farming , as well as on public land used at the time as stockyards and railway sidings.

Many of these activities – for example, the use of dieldrin in sheep dips and to kill insects in the 1940s to the 1960s – were not considered to be hazardous at the time.

More about contamination from timber treatment

Chemical treatment has been used for many years in New Zealand for preserving timbers, as softwoods such as radiata pine are prone to attack by fungi and insects.

The first timber preservative used in this country was creosote derived from coal tar. After the production of organochlorine pesticides in the late 1940s and 1950s, the timber industry made widespread use of pentachlorophenol (PCP) to combat sapstain fungi. Chlordane and dieldrin were used in the glue of some manufactured wood products. Significant use of these organochlorines in the timber industry ceased in 1988 and they were formally deregistered for these purposes by the end of 1991.

Since the 1970s the timber preservatives in common use have included boron, CCA (a formulation of copper, chromium and arsenic salts), and light organic solvent preservatives (LOSP).

Soil contamination and Ministry work

Soil contamination has occurred to varying extents at many of New Zealand's sawmill and timber treatment sites, some of which have now ceased to operate. Contamination would generally be caused by the cumulative effect of drips, leaks, spills and waste disposal practices during an era when less emphasis was placed on the containment of potentially hazardous chemicals.

The Ministry for the Environment also produced the Health and Environmental Guidelines for Selected Timber Treatment Chemicals. These guidelines provide owners, occupiers, regulators and assessors of sawmill and timber treatment sites with detailed, practical advice on assessing and managing these sites. The Ministry worked with experts from central and local government, the timber industry, scientists and consultants to develop the guidelines.

More about contamination from gas production

There are around 54 gasworks or former gasworks sites in New Zealand. Between the late 1800s and 1988, gasworks were a familiar sight in towns and cities throughout New Zealand. During this time the production of gas from coal was a major source of fuel for heating, cooking and lighting.

When a national natural gas reticulation system was set up during the 1970s and 1980s, these gasworks were gradually closed.

Soil contamination and Ministry guidelines

The manufacturing process generated a number of by-products and wastes, such as coal tar, spent oxide, purifier waste, ash and clinker. These wastes contain substances that are potentially hazardous to human health. Many of these wastes were disposed of both on and off-site. When many of the sites were closed, underground structures containing many of these contaminants were left.

When is contaminated land a problem?

Contaminated land is a problem when the hazardous substances are at a concentration and/or are located where they have, or are reasonably likely to have, a significant adverse effect on human health and the environment. Contaminated land is a more urgent problem when contaminants are close to buildings and people, or close to water bodies and important habitats.

People, animals and the environment can be exposed to hazardous substances on contaminated land by:

direct contact with contaminated soil

swallowing food or water from contaminated environments

breathing vapours or contaminated dust .

As well as endangering health, these substances can:

limit the use of land

cause corrosion that may be threaten building structures

reduce land value.

As land is increasingly developed in New Zealand, it is important to know where contaminated land is located so people are not exposed to contaminants that may affect their health.

To help with identifying potentially contaminated land, the Ministry of the Environment has compiled a list of activities and industries commonly associated with contaminated land This list is called the Hazardous Activities and Industries List (HAIL).

Local authorities may use the HAIL to identify potentially contaminated sites. Further investigation of an individual site is required to determine whether the site is contaminated.